What causes the seasons?

It turns out that the elliptical orbit of the Earth has little effect on the seasons. Instead, it is the 23.45-degree tilt of the planet's rotational axis that causes us to have winter and summer.

The diagram below demonstrates what happens.


In this diagram, you can see the axis of rotation and the equator. The Northern Hemisphere (at the top) is currently experiencing winter, and the Southern Hemisphere is experiencing summer. By looking at how sunlight is landing on the planet in the diagram, you can clearly see two things:

  • The Southern Hemisphere is getting about three times as much sunlight as the Northern Hemisphere.
  • The North Pole is getting zero sunlight, which is why it experiences 24 hours of darkness in January.

That huge difference in the amount of sunlight reaching the ground in the different hemispheres is what causes the seasons.

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